I have not seen the US threaten the use of nuclear weapons. Their doctrine has stayed the same for decades and speaks of using nukes only in nukes are used against them or a credible launch of such is detected.
As usual, you're trailing the events, or maybe just outright lie...that's not true since at least Obama (although history shows us that USA have
no problems nuking civilians)
https://www.armscontrol.org/act/2022-04/news/biden-policy-allows-first-use-nuclear-weapons